Bidirectional Magnetic Position Sensor Having Field Rotation

ABSTRACT

The disclosure relates to a magnetic position sensor in at least two directions, the sensor including at least one magnetized element and a probe including at least two magneto-sensitive elements located substantially on the same point and each measuring one of the components of the magnetic field generated by the magnetized element, the magnetized element being movable relative to the magneto-sensitive elements. The probe includes at least one processing circuit capable of carrying out angle and module calculations on the basis of algebraic combinations of the components of the magnetic field and providing at least two independent signals representing the position of the movable element along, respectively, one and the other of the two directions. According to the disclosure, the magnetization vector of the magnetized element is variable in relation to the normal vector on the surface of the magnetized element that is placed opposite the probe in at least one of the dimensions of the magnetized element so as to define a single position of the probe in relation to the magnetized element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International ApplicationNo. PCT/FR2010/052320, filed on Oct. 28, 2010, which claims priority toFrench patent application Ser. No. 09/05356, filed on Nov. 6, 2009, bothof which are incorporated by reference herein.

TECHNICAL FIELD

The present invention concerns the field of contactless magneticposition sensors the purpose of which is to supply simultaneously twoindependent output signals representing a position in two directions(translation and translation, translation and rotation, rotation androtation. Sensors that detect the position from a magnetic field havemany advantages:

-   -   no mechanical contact with the moving part, and therefore no        wear,    -   insensitivity to dirt,    -   reduced production costs,    -   long service life.        The majority of contactless magnetic position sensors are in        only one direction (a rotation OR a translation) but more and        more applications are being seen to appear where a sensor in two        directions (bidirectional sensor) is necessary, such as for        example for detecting the position of transmission members or        generally a rotation and a translation are combined. In such        applications it is particularly important to have position        information in a direction that is not dependent on the position        in the other direction (independent output signals).

BACKGROUND

The majority of bidirectional sensors already existing use permanentmagnets associated with a more or less complex magnetic circuit, madefrom ferromagnetic material used to guide and/or concentrate themagnetic flux generated by the permanent magnet or magnets, but to thedetriment of the cost and performance of the sensor. Thus, in the priorart, the patent FR 2786266 of the applicant is known, relating to aposition sensor in two directions but in which the space requirement andthe surface area of the magnet used limit the practical use of thissensor for long travels. This sensor also has high hysteresis due to theferromagnetic stators and the measurement depends on the variation inthe remenant induction, which must therefore be compensated for.

Moreover, European patent EP 800055 describes a linear angular positionsensor. This sensor delivers analogue signals that are difficult to usesince they are non-linear and of a low level. Such sensors requireseveral separate measuring points for measuring the relative position intwo directions. In addition, they require stator parts that contributehysteresis and the sensitive elements measure the amplitude of the fieldand are therefore sensitive to geometric tolerances and temperature. TheU.S. Pat. No. 4,639,667 or WO 9716736 describe sensors functioningaccording to principles that do not make it possible to deliver linearand independent signals representing the position in two dimensions.

There also exist bidirectional sensors that are merely the putting endto end of two independent unidirectional sensors, such as for examplethe patent WO 2008138662 and the U.S. Pat. No. 6,175,233 describing twolinear sensors that each measure one direction. For each sensor there isa magnet and an element for detecting the magnetic field, theconsequence of which is to lead to a high space requirement and highproduction cost. In addition, these sensors measure the amplitude of thefield and are therefore also sensitive to geometric tolerances andtemperature.

There are also known, in the prior art, the U.S. Pat. No. 7,421,923 andU.S. Pat. No. 7,293,480, which are sensors for detecting gears engagedby a gear lever. Such patents present a solution for detecting positionsin two directions but use a magnet and at least as many Hall sensorspositioned in space as there are gears to detect. It is thereforenecessary to use an array of sensors for discriminating single positionsand to obtain a digital detection of the gears. The multiple number ofsensors means that this solution is expensive to implement and does notoffer means for knowing the intermediate positions.

To remedy the problems relating to the position detection by measuringamplitude described above, there exist position sensors that measure therotation of the magnetic field, in other words the direction thereof,rather than the amplitude thereof. However, this applies mainly tounidirectional rather than bidirectional sensors.

There are known for example in the prior art sensors as described in thepatents FR 2898189 and FR 2909170 of the applicant, which use thedirection of the field rather than the amplitude for detecting arelative position between a magnet and a magnetosensitive probe. Thismeasurement of direction makes it possible to be insensitive totemperature and to mechanical clearances and does not use anyferromagnetic part and therefore does not have magnetic hysteresis.However, such sensors measure only one magnetic field direction via thecalculation of a single amplitude ratio from two components of themagnetic field, and can therefore know the relative position of amovable magnet with respect to a magnetosensitive probe only in onedirection rather than two. Likewise, the patents and patent applicationsU.S. Pat. No. 6,731,108, U.S. Pat. No. 6,960,974 and WO 2004015375afford only measurement of the linear movement of a magnet with respectto one or more magnetosensitive elements using the field direction.However, for practical implementation of travels greater than 20-25 mm,these sensors require several probes placed on the various parts of thetravel, which increases the cost of the sensor and requires precisepositioning of the probes.

Solutions are however known in the prior art for measuring bidirectionalposition and using the measurement of the rotation rather than of theamplitude of the magnetic field but, in the case of very specificapplications to control levers (joysticks). Thus the patent applicationsUS 2007024043 or US 20090062064 describe sensors for joysticks thatcomprise a simple magnet magnetised unidirectionally, along itsthickness, and a probe that measures only two components of the fieldand therefore a single field direction (the angle formed by the twocomponents). This principle does not make it possible to deliverindependent linear signals in two directions. Systems of the joysticktype are in addition limited only to rotations and cannot measuretranslations. Moreover, the angle that can be detected by such ajoystick system is limited to around 30 degrees. Beyond this, the magnetis situated very far away from the probe, which no longer sees enoughmagnetic field to deduce a position therefrom. In fact, for a practicalimplementation for travels greater than 40 degrees, these sensorsrequire several probes based on the different parts of the travel, whichincreases the cost of the sensor.

There is also found in the prior art a Melexis application note for ameasurement of two rotation angles (http://ww.melexis.com/Sensor ICsHall effect/Triaxis Hall ICs/MLX90333 648.aspx) where two joystickconfigurations are presented. The first is a solution where the centreof rotation of the bipolar magnet is merged with the measuring point,which requires a complex and bulky mechanical system that cannot easilybe integrated in an application. The second configuration presents asolution where the centre of rotation of the magnet is situated behindthe magnet (the magnet is between its centre of rotation and thesensitive elements). In this case, the three components of the magneticfield are used to determine two rotation angles. The magnet used is acylinder with a very small diameter with a magnetisation that isconstant in amplitude and direction along its thickness. That is to saythe magnetisation of the magnet at any point on this magnet has the samemodulus and is perpendicular to the top and bottom faces of the magnet.This very specific configuration is intended only for measuring twoangles and for very short travel (around 30 degrees). This is because,in order to be able to detect the rotation of the magnet with thealgorithm used, it is necessary for the diameter of the magnet to besmall (theoretically a punctiform magnet with radial magnetisation),which means that, as soon as we have a small rotation of the magnet, themagnet moves away from the magnetosensitive elements and the magneticinduction becomes too small at the magnetosensitive elements of theprobe to have precise detection of the rotation of the magnet. This iswhy this type of system requires a magnet with very high remanence(typically Br>1.2 T) and very thick (thickness >10 mm), which istherefore expensive and difficult to magnetise, with what is in additiona large axial thickness (typically >10 mm), which causes a problem ofspace requirement. In addition, with these solutions, the mechanical airgap between the surface of the flat magnet and the measuring pointvaries according to the rotations of the magnet, which involvesdeterioration in linearity and a larger air gap than necessary to avoidcollision of the edges of the magnet with the probe support. The idealthing for preventing this is a magnet with a very small diameter butwhich poses the problems already mentioned above.

SUMMARY

The invention presented here therefore proposes in particular to remedy,in a simple and efficient manner, the problems of bidirectional sensorsdisclosed above (limited travel, measurement only of rotations, magnetsof high remanence and thick, high space requirement and cost, etc). Inparticular, we propose an absolute position sensor in any two directions(translation-translation, translation-rotation or rotation-rotation)measuring the relative movement between a magnetised element and amagnetosensitive probe measuring at least two components of the magneticfield substantially at the same point, without any high or low travellimitation and preferentially using the measurement of the direction ofthe magnetic field rather than the amplitude thereof.

More precisely, we propose a magnetic position sensor in at least twodirections comprising at least one magnetised element (1) and a probe(6) comprising at least two magnetosensitive elements (2) and (3)located substantially at the same point and each measuring one of thecomponents of the magnetic field generated by the said magnetisedelement (1), the magnetised element (1) being able to move relative tothe said mangetosensitive elements (2) and (3), and at least oneprocessing circuit (5) able to make calculations of angles and modulifrom algebraic combinations of the components of the magnetic field andsupplying at least two independent signals representing the position ofthe movable element in respectively each of the two directions,characterised in that the magnetisation vector of the magnetised element(1) is variable with respect to the vector normal to the surface of themagnetised element disposed opposite the probe (6) on at least one ofthe dimensions of the said magnetised element so as to define a uniqueposition of the said probe (6) vis-à-vis the said magnetised element(1).

This variation in the magnetisation vector can be obtained by varyingthe direction thereof along at least one of the dimensions thereof. Inthis case, the direction of the magnetisation vector may have severalperiods over the travel measured. This variation in the magnetisationvector can also be obtained by varying one of the dimensions of themagnetised element along at least one of the two directions causing avariation in the direction of the vector normal to the surface. In thiscase, the dimension may vary according to a discontinuous function oraccording to a continuous function of the sinusoidal type. Thisvariation in the magnetisation vector may also be obtained by varyingthe amplitude thereof along at least one of the two directions.

In all these cases, the magnetisation vector has at least onealternation in direction in at least one of the two directions. In allthese cases, the signal processing circuit can make at least twoarctangent calculations or at least one arctangent calculation and onemodulus calculation. In all these cases, the signal processing circuitcan also carry out an arctangent calculation of the ratio of twocomponents of the magnetic field after having applied a correctioncoefficient between these two components.

In a variant of the invention, the processing circuit is integrated withthe magnetosensitive elements in a single component. In a variant of theinvention, the magnetised element consists of a permanent magnet and atleast one ferromagnetic part. Finally, preferentially, the components ofthe measured magnetic field vary in a substantially sinusoidal fashionin each of the at least two directions.

In general terms, this sensor has a single magnetised element,preferentially a permanent magnet of the rare earth type (SmCo, NdFeB)or ferrite type, thin and with a length and width substantiallyequivalent to the required travel, without any limitation in travelother than the size of the magnet. The fact that this sensor uses only asingle magnetosensitive probe measuring the three components of themagnetic field at a single point thus leads to a minimum spacerequirement and limited cost. This sensor uses the ratios of amplitudesbetween the components of the magnetic field in order to be free of thevariations in the magnetic properties of the magnet according totemperature and time and also so as not to be sensitive to geometrictolerances and variations in air gap, which makes it possible to proposean extremely robust solution. This sensor does not have anyferromagnetic parts that are fixed with respect to the magnetosensitiveelements and therefore no magnetic hysteresis, while guaranteeingsimplicity of the structure. Finally, the sensor provides independentposition information for each of the two directions, with very greatprecision.

The functioning of the sensor is defined more precisely as follows:

Let M be the point where the magnetosensitive elements are groupedtogether and measure the three components of the magnetic field and O′the midpoint of the external surface of the magnetised element (1) thatis opposite the probe (6) where the magnetosensitive elements areintegrated. A point O will be used in the case where at least one of thetwo directions is a rotation with, in this case, O the centre ofrotation. We can thus write the following vector equation:

{right arrow over (OM)}={right arrow over (OO′)}+{right arrow over(O′A)}+{right arrow over (AM)}

The vector {right arrow over (OO′)} is constant, and depends only on thegeometry of the magnet, the norm of this vector corresponds to theexternal radius of the magnet in the case of a tile or spherical magnetand is zero in the case of a parallelepipedal magnet. The vector {rightarrow over (AM)} is constant and is oriented along the thickness of themagnet, that is to say {right arrow over (AM)}=Z_(O) n, Z_(O), z₀ iscommonly referred to as the air gap between the magnetised element andthe point M that groups together the magnetosensitive elements. Thus{right arrow over (OA)}={right arrow over (x^(i))}+{right arrow over(y^(j))} is defined as being the vector that represents the position ofthe magnetised element with respect to the magnetosensitive elements inthe two directions of the movable element that are oriented along {rightarrow over (i)} and j. For reasons of simplicity, the directions will bedenoted X and Y hereinafter and correspond to the relative movementsalong {right arrow over (i)} and {right arrow over (j)}.

The two directions X and Y can thus be two translations where X and Ycorrespond to a length, or may be a translation and a rotation where xthen corresponds to the length and y to an angle and finally the twodirections may be two rotations where x and y both correspond to angles.In order to determine the position of the magnetised element withrespect to the magnetosensitive elements in the two directions X and Yof the movable element, it is therefore necessary to determine thecoordinates x and y.

In general terms, whether it be for a rectilinear, cylindrical orspherical magnet, hereinafter the thickness corresponds to the dimensionof the magnet oriented along the unit vector {right arrow over (n)}normal to the top surface of the magnet, the length corresponds to thedimension of the magnet oriented by the vector {right arrow over (i)}tangent to the top surface of the magnet and the depth corresponds tothe dimension of the magnet oriented by the vector {right arrow over(j)} also tangent to the top surface of the magnet and perpendicular tothe vector {right arrow over (i)}. In the case of a rectilinear,cylindrical or spherical magnet, the reference frame ({right arrow over(i)} {right arrow over (j)} {right arrow over (n)}) used is respectivelya Cartesian, polar or spherical reference frame.

According to a first embodiment, the sensor consists of a magnetisedelement (preferentially a permanent magnet) generating a magnetic fieldthe normal component (along {right arrow over (n)}) on the one hand andthe tangential (along {right arrow over (i)}) and transverse (along{right arrow over (j)}) components on the other hand, measured on itssurface, vary periodically (according to reference mechanical periodscalled λx and λy), the effective variation along the surface being ableto correspond to one or more whole periods or fractions of periods.According to a preferred configuration, the magnetised element will havea length and depth substantially similar to the travels used as well asa magnetisation the direction of which varies substantially linearly inthe two directions X and Y thereof and with respect to its thickness,its length AND its depth.

This means that, at any point A on the external surface of themagnetised element, the angle between the magnetisation vector {rightarrow over (M)} and the normal vector {right arrow over (n)}, that is tosay {right arrow over (M)}, {right arrow over (n)}, and the anglebetween the magnetisation vector {right arrow over (M)} and the vector{right arrow over (i)}, that is to say {right arrow over (M)}, {rightarrow over (i)}, vary linearly in the direction X AND the angle betweenthe magnetisation vector {right arrow over (M)} and the normal vector{right arrow over (n)} {right arrow over (M)}, {right arrow over (n)}and the angle between the magnetisation vector {right arrow over (M)}and the vector {right arrow over (j)} vary linearly in the direction Y.In the vicinity of this magnetised element, this magnetisation generatesa magnetic field {right arrow over (B)}({right arrow over (B)}=Bxī+Byj+Bz n) the tangential (Bx), normal (Bn) and transverse (By) componentsof which are substantially sinusoidal, over a major part of the travelin the directions X and Y.

We will therefore consider a magnet of length Lx, width Ly and thicknessLz, and M(x,y,z₀) a point of measurement of the components Bx, By, Bz ofthe magnetic field generated by the magnetised element. +/−y_(max) isthe maximum travel that we wish to measure in the direction Y, y_(max)being less than, equal to or greater than the width of the magnetisedelement. +/−x_(max) is the maximum travel that we wish to measure in thedirection X, x_(max) being less than, equal to or greater than thelength of the magnetised element.

We wish to know the position along X and Y, that is to say x and y. z₀corresponds to the measurement air gap between the movable element andthe fixed element. The components By and Bz of the magnetic field havethe same phase along X, whereas the component Bx is out of phase by aquarter of a period. In this first embodiment, the magnetisationgenerates a magnetic field such that we can write as follows thecomponents of the magnetic field at M(x,y,z₀):

${{{{{{{{{{Bx}\left( {x,y,z_{o}} \right)} = {{Bx}\; {MAX}*{\cos \left( {{\frac{2\pi}{\lambda_{x}}*x} + \varphi} \right)}*{\cos\left( \frac{2\pi}{\lambda_{x}} \right.}}}\left. * \right)}*\frac{A}{z_{o}}}{{{By}\left( {x,y,z_{o}} \right)} = {{By}\; {MAX}*{\sin \left( {{\frac{2\pi}{\lambda_{x}}*x} + \varphi} \right)}*{\sin\left( \frac{2\pi}{\lambda_{x}} \right.}}}}\left. * \right)}*\frac{A}{z_{o}}}{{{Bz}\left( {x,y,z_{0}} \right)} = {{Bz}\; {MAX}*{\sin \left( {{\frac{2\pi}{\lambda_{x}}*x} + \varphi} \right)}*{\cos\left( \frac{2\pi}{\lambda_{x}} \right.}}}}\left. * \right)}*\frac{A}{z_{o}}$

where λx and λy are respectively the wavelengths for which the magneticfield turns through 360 degrees along respectively X and Y and A anon-zero constant particular to each sensor that depends on the air gapbetween the surface of the magnetised element and the magnetosensitiveelements as well as the geometry of the magnetised element.

For this first preferred embodiment, the magnetisation is normal to thecentre of the magnet at O′, and therefore we have

     φ = ? ?indicates text missing or illegible when filed

The magnetisation may, for example, turn through 360 degrees along X andY. This means that the magnetisation turns through 360 degrees over thelength of the magnetised elements and 360 degrees over the width of themagnetised element, which in this case gives us λx=Lx and λy=Ly. We thenhave at any point M(x,y,z₀) above the magnetised element:

${{Bx}\left( {x,y,z_{o}} \right)} = {{Bx}\; {MAX}*{\cos \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}*{\cos \left( {\frac{2\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}}$${{By}\left( {x,y,z_{o}} \right)} = {{By}\; {MAX}*{\sin \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}*{\sin \left( {\frac{2\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}}$${{Bz}\left( {x,y,z_{o}} \right)} = {{Bz}\; {MAX}*{\sin \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}*{\cos \left( {\frac{2\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}}$

Naturally, according to the magnetic field generated by the magnetisedelement, the wavelength λy can be much greater than the width of themagnetised element Ly as for FIGS. 4, 5 and 6, where λy is larger thanthe width Ly, which means that the magnetised field turns through lessthan 360 degrees over the width of the magnetised element.

If the components Bx, By and Bz of the magnetic field are measured atany point M in the space that surrounds the magnetised element, it ispossible to know the position in the directions X and Y by applying thefollowing formulae in order to deduce x and y therefrom. Thismeasurement of the three magnetic components can be carried out forexample by three magnetosensitive elements located at the same point andintegrated in the same package called a probe (6) using components ofthe MLX90333 or HAL3625 etc type. From these three components we canmake the following calculation (FIG. 9):

a tan(kxBz/Bx)

a tan t(kyBz/By)

with: Bx, By, Bz components of the magnetic field measured at point M ofcoordinates x,y,z0 and kx, ky correcting gain coefficients allocated tothe measurement of the field components to standardise the components.This calculation can be made inside a single component that comprisesthe magnetosensitive element or then can be carried out by an elementexternal to the probe (microcontroller, microprocessor, ECU, etc).

By applying these formulae there are obtained:

${{Atan}\; {t\left( {{kx}\frac{Bz}{Bx}} \right)}} = {{{atan}\left( {\left( {{kx}*{Bz}\; {MAX}*{\sin \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}*{\cos \left( {\frac{2\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}} \right)/\left( {{Bx}\; {MAX}*{\cos \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}*{\cos \left( {\frac{2\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}} \right)} \right)} = {{atan}{\quad\left( {{\left( {{kx}*{Bz}\; {MAX}*{\sin \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}} \right)/\left( \left( {{Bx}\; {MAX}*{\cos \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}} \right) \right)} = {{atan}\left( {{{kx}*\frac{{Bz}_{\max}}{{Bx}_{\max}}*{\tan \left( {{\frac{2\pi}{L_{x}}*x} + \frac{\pi}{2}} \right)}} = {{{\frac{2\pi}{L_{x}}*x} + {\frac{\pi}{2}{avec}\; {kx}}} = \frac{{Bx}_{\max}}{{Bz}_{\max}}}} \right.}} \right.}}}$

with

A tan(kx Bz/Bx) is therefore the linear function of variable x and theevaluation thereof by calculation enables us to determine the value xand therefore the position in the direction X of the point M withrespect to the centre of the magnetised element O′. M being the pointwhere the magnetosensitive elements are placed, we thus know therelative position of the magnetised element with respect to themagnetosensitive elements. The relative position along X is thereforeindependent of the temperature and air gap and can be determined withhigh precision (typically less than 1% of the full travel). So that thisoutput is equal to zero when x=0, this can be done via programming ofthe probe (6) since the slope and the ordinate at the origin depend onthe magnet and its magnetisation only and are therefore programmable.

We can likewise calculate arctan(ky Bz/By)

${{Atan}\left( {{ky}\frac{Bz}{By}} \right)} = {{{\frac{2\pi}{L_{y}}*y} + {\frac{\pi}{2}\mspace{14mu} {avec}\mspace{14mu} {ky}}} = \frac{{By}_{\max}}{{Bz}_{\max}}}$

This leads to the relative position in the direction Y of the magnetisedelement with respect to the magnetosensitive elements, as explainedpreviously for the position along X. Consequently such a magnetisationand such a processing of the signals as described in this firstembodiment enable us to determine the relative position in twodirections X and Y of the magnetised element with respect to themagnetosensitive elements from the three components of the magneticfield measured at the same point M. We can also, with the samemagnetisation, use the following postprocessing:

${{Atan}\left\lbrack \frac{\sqrt{\left( {{{Kz}*{Bz}^{2}} + {{Ky}*{By}^{2}}} \right.}}{Bx} \right\rbrack}\mspace{14mu} {and}\mspace{14mu} {{Atan}\left\lbrack \frac{\sqrt{\left( {{{Kz}*{Bz}^{2}} + {{Kx}*{Bx}^{2}}} \right.}}{Bx} \right\rbrack}$

According to a second embodiment, the present invention consists of amagnetised element (preferentially a permanent magnet) generating amagnetic field, the normal component (along {right arrow over (n)}) onthe one hand and the tangential (along {right arrow over (i)}) andtransverse (along {right arrow over (j)}) components on the other hand,measured at the surface thereof, varies periodically (according toreference mechanical periods called λx and λy, the effective variationalong the surface being able to correspond to one or more whole periodsor factions of periods. According to this second embodiment, themagnetised element will have a magnetisation where the direction variessubstantially linearly along only one of its two directions and withrespect to its thickness AND its length. This means that, at any point Aon the magnetised element the angle between the magnetisation vector{right arrow over (M)} and the normal vector {right arrow over (n)},that is to say ({right arrow over (M)}, {right arrow over (n)}) and theangle between the magnetisation vector {right arrow over (M)} and thevector {right arrow over (i)}, that is say ({right arrow over (M)},{right arrow over (i)}) vary linearly in the direction X, but that theangle between the magnetisation vector {right arrow over (M)} and thevector J is constant in the direction Y.

This second embodiment requires a narrow magnetised element (<30 mm orequivalent in terms of angle) so that, in the vicinity of thismagnetised element, this magnetisation generates a magnetic field thetangential (Bx), normal (Bn) and transverse (By) components of whichwith respect to the magnet are substantially sinusoidal over a majorpart of the travel and are of the same form as the components of thefirst embodiment. A narrow magnet enables us, by virtue of the edgeeffects, to obtain a magnetic field at M that varies in the direction Ywithout for all that the magnetised element having a variablemagnetisation in this direction. For this second preferred embodiment,the magnetisation may be normal, tangential or other at the centre ofthe magnet at O′, and therefore in this case we have φ=[0;2π], themagnetisation may turn through 360 degrees in the direction X but willturn by less than 180 degrees in the direction Y, which gives us forexample λx=Lx and λy=2Ly.

We then have, at any point M(x,y,z₀) above the magnetised element:

${{Bx}\left( {x,y,z_{o}} \right)} = {{Bx}\; {MAX}*{\cos \left( {{\frac{2\pi}{L_{x}}x} + \varphi} \right)}*{\cos \left( {\frac{\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}}$${{By}\left( {x,y,z_{o}} \right)} = {{By}\; {MAX}*{\sin \left( {{\frac{2\pi}{L_{x}}x} + \varphi} \right)}*{\sin \left( {\frac{\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}}$${{Bz}\left( {x,y,z_{o}} \right)} = {{Bz}\; {MAX}*{\sin \left( {{\frac{2\pi}{L_{x}}x} + \varphi} \right)}*{\cos \left( {\frac{\pi}{L_{y}}*y} \right)}*\frac{A}{z_{o}}}$

In the same way as for the first preferred embodiment, we can calculatea tan(kx Bz/Bx) and Bz/By) and thus obtain:

${{Atan} = {{\frac{2\pi}{L_{x}}*x} + \varphi}},$

the output of this function will vary from 2π over the travel of lengthLx

${{Atan} = {{\frac{\pi}{L_{y}}*y} + \varphi}},$

the output of this function will vary solely by π over the travel oflength Ly.

We can also, in this embodiment, calculate the arctangent in order todetermine the position along X and, knowing this position, we can useonly the value of the component By in order to derive therefrom theposition along Y. This postprocessing does however have the disadvantageof using directly a component, which means that this solution will besensitive to the variation in air gap z₀ and to the temperature but isvery suitable when there are only a few discrete positions to bedetermined, such as for a gearbox application where only the knowledgeof the 6 or 7 gears over a given range is necessary and where theintermediate positions do not need to be known.

According to a third preferred embodiment, the magnet will have amagnetisation the direction of which is constant and for which themagnetisation vector {right arrow over (M)} any point on the magnetisedelement is colinear with {right arrow over (n)} or {right arrow over(i)} or {right arrow over (j)}, in other words the magnetisation isalong the thickness, the length or the width of the magnetised element.On the other hand, the magnetised element will have a thickness thatvaries almost sinusoidally along its two directions X and Y. This almostsinusoidal variation in thickness over a half period combined with auniform magnetisation generates a magnetic field above the magnet thecomponents of which are substantially sinusoidal and are expressed in asimilar fashion to the case of the first embodiment described above.According to this third preferred embodiment, the magnetic fieldgenerated by this magnetised element will turn only by approximately 180degrees in the directions X and Y, which give us for example λx=2Lx andλy=2Ly. The processing of the two components will be identical to thefirst embodiment in order to determine x and y.

According to a fourth embodiment, the magnetised element will have amagnetisation the direction of magnetisation of which is constant andfor which the magnetisation vector {right arrow over (M)} at any pointon the magnet is colinear with {right arrow over (n)} or {right arrowover (i)} or {right arrow over (j)}, in other words the magnetisation isalong the thickness, the length or the width of the magnetised element.On the other hand, the magnetised element will have a thickness thatvaries almost sinusoidally along only one of its two directions X or Y.This fourth embodiment requires a thin magnet (<30 mm or equivalent interms of angle) so that, in the vicinity of this magnetised element,this magnetisation generates a magnetic field the tangential (Bx),normal (Bn) and transverse (By) components with respect to the magnetare substantially sinusoidal, over a major part of the travel, and areof the same form as the components of the first embodiment. A narrowmagnetised element enables us, by virtue of the edge effects, to obtaina magnetic field at M that varies in the direction Y without for allthat the magnetised element needing its thickness to vary in thedirection Y.

In the same way as for the third preferred embodiment, the magneticfield generated by this magnetised element turns only by approximately180 degrees in the directions X and Y, which gives us for example λx=2Lxand λy=2Ly. The processing of the components is identical to the firstembodiment for determining the positions x and y.

According to a fifth embodiment, the magnetised element will have amagnetisation the direction of which varies substantially linearly inonly one of its two directions and with respect to its thickness AND itslength. This means that, at any point A on the magnetised element, theangle between the magnetisation vector {right arrow over (M)} or {rightarrow over (n)} or and the normal vector ({right arrow over (M)}, {rightarrow over (n)}), that is to say {right arrow over (M)}, and the anglebetween the magnetisation vector {right arrow over (i)} and the vectorthat is to say ({right arrow over (M)}, {right arrow over (i)}) varieslinearly in the direction X but that the angle between the magnetisationvector {right arrow over (M)} and the vector {right arrow over (j)} isconstant in the direction Y. In addition, unlike the second embodiment,the magnetised element has a variation in its thickness along only oneof its two directions (Y) and varies according to a discontinuousfunction in the form of a staircase.

In this case we can use only the components Bx and Bz of the magneticfield and carry out the following postprocessing:

A tan(kyBz/By) and ∥Bxī+Bz j∥=√{square root over (Bx² +Bz ²)}

Calculation of the angle gives us very precise information on the linearposition along X and the modulus gives us rough position information inthe direction Y, given that we have a magnet in the form of a staircase.This solution may however be very useful when we have a probe with onlytwo measurable components such as MLX90316 or the like and makes itpossible to discretise positions along Y. The number of stairs that themagnet has along Y corresponds typically to the number of positions thatwe can discretise. This embodiment can be used for discriminating gearsin a gearbox application for example.

According to a sixth embodiment, the magnetised element has amagnetisation the direction of which is constant preferentially alongits thickness, without this being exclusive. This means that themagnetisation vector M at any point on the magnet is colinear with{right arrow over (n)}. On the other hand, the amplitude of themagnetisation vector varies linearly along one or two of its twodirections. This means that, at any point A on the magnetised element,the magnetisation vector {right arrow over (M)} is oriented along thethickness of the magnet but the amplitude of this vector variessinusoidally along one or two of its directions X and Y. We willtherefore have:

{right arrow over (M)}=A(x,y){right arrow over (n)} with A(x,y)=A ₁sin(x)+A ₂ sin(y)+constante,

A1 and A1 being constants that depend on the magnetised element.

According to a seventh embodiment, which applies to the cases where atleast one direction is a rotation (it would be denoted Y), the presentinvention consists of a magnetised element in the form of a tile.According to this embodiment, the magnetised element will have diametralmagnetisation where the magnetisation direction varies substantiallylinearly along its rotation direction Y and with respect only to itsthickness. This means that, at any point A on the magnetised element,the angle between the magnetisation vector {right arrow over (M)}, andthe normal vector {right arrow over (n)}, that is to say ({right arrowover (M)}, {right arrow over (n)}) varies linearly in the direction ofrotation Y and that the angle between the magnetisation vector {rightarrow over (M)} and the vector {right arrow over (i)}, that is to say({right arrow over (M)}, {right arrow over (i)}), is constant in thedirection X, X being a translation direction. In addition, a diametralmagnetisation means that the magnetisation vectors {right arrow over(M)} at each point A on the magnetised element {right arrow over (M)}are colinear, as shown by FIG. 19.

This embodiment requires a short magnetised element (<30 mm orequivalent in terms of angle) so that, in the vicinity of thismagnetised element, this magnetisation generates a magnetic field thetangential (Bx), normal (Bn) and transverse (By) components of whichwith respect to the magnet are substantially sinusoidal over a majorpart of the travel and are of the same form as the components of thefirst embodiment. A short magnetised element enables us, by virtue ofthe edge effects, to obtain a magnetic field at M that varies in thedirection X without for all that the magnetised element having amagnetisation that is variable in this direction. According to thispreferred embodiment, the magnetisation may be normal, tangential orother at the centre of the magnet at O′, and therefore in this case wehave φ=[0;2π], the magnetisation turning approximately as much as theangle of the magnet tile. That is to say, if we have a tile of 90degrees, the components of the magnetic field generated by this tileturn by approximately 90 degrees.

According to an eighth embodiment, the magnetised element has a lengthand depth substantially adjacent to the useful travels as well as amagnetisation the direction of which varies discontinuously in the twodirections. At any point A on the magnetised element, the angle betweenthe magnetisation vector {right arrow over (M)} and the normal vector{right arrow over (n)}, that is to say ({right arrow over (M)}, {rightarrow over (n)}), alternates between 0 degrees and 180 degrees in thedirection X or in the two directions X and Y as in FIG. 20. In thevicinity of this magnetised element, this magnetisation generates amagnetic field {right arrow over (B)}({right arrow over (B)}=Bxī+By j+Bzn) the tangential (Bx), normal (Bn) and transverse (By) components ofwhich with respect to the magnet are substantially sinusoidal over amajor part of the travel in the directions X and Y, and, by applying thesame postprocessing of the components as in the first embodiment, we canderive therefrom the position of the magnetised element with respect tothe magnetosensitive elements in the two directions X and Y. Naturallythese embodiments are non-exhaustive and other magnetisation or magnetgeometry configurations are possible.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be understood better from a reading of the followingdescription with reference to the following figures:

FIG. 1 shows a solution of the prior art.

FIGS. 2 a, 2 b and 2 c show the various geometric forms of themagnetised element and the associate reference frames.

FIG. 3 shows an embodiment where the sensor is composed of aparallelepipedal magnetised element and a probe.

FIG. 4 shows the component Bx of the magnetic field obtained with amagnetisation according to one of the embodiments described by thispresent invention.

FIG. 5 shows the component Bz of the magnetic field obtained with amagnetisation according to one of the embodiments described by thispresent invention.

FIG. 6 shows the component By of the magnetic field obtained with amagnetisation according to one of the embodiments described by thispresent invention.

FIG. 7 shows the change along the axis X of the component By of themagnetic field, for several positions y.

FIG. 8 shows the processing of the magnetic field in order to derivetherefrom the two positions in the two directions.

FIGS. 9 a, 9 b, 9 c show various algorithms for postprocessing of thecomponents Bx, By, Bz in order to determine the position x and y of themoving object along X and Y.

FIG. 10 shows an output signal according to one embodiment of thepresent invention that makes it possible to determine the position alongthe direction X independently of the position along Y.

FIG. 11 shows an output signal according to one embodiment of thepresent invention that makes it possible to determine the position alongthe direction Y independently of the position along X.

FIG. 12 is a plan view of a rectilinear magnetised element of constantthickness that has a sinusoidal magnetisation in several directionsaccording to one embodiment of the present invention.

FIG. 13 is a perspective view of a magnetised tile element of constantthickness that has sinusoidal magnetisation in several directions whereX is a rotation and Y a translation.

FIG. 14 shows a thin rectilinear magnetised element of constantthickness and a continuous sinusoidal magnetisation in the direction Xaccording to one embodiment of the present invention.

FIG. 15 shows a circular magnetised element of variable thicknessquasi-sinusoidally along several directions and magnetised substantiallythrough the thickness.

FIG. 16 shows a rectilinear magnetised element with variable thicknessquasi-sinusoidally in its direction X and magnetised substantiallythrough its thickness.

FIG. 17 shows a magnet the thickness of which varies discontinuously inthe direction Y and has sinusoidal magnetisation in the direction X.

FIG. 18 is a side and plan view of a magnetised element the thickness ofwhich is constant and which has magnetisation through its thickness butthe amplitude of which is sinusoidal in the direction X.

FIG. 19 is a perspective view of a tile magnetised element of constantthickness and diametral magnetisation, where the direction X is arotation and the direction Y is a translation.

FIG. 20 is a view in section and perspective of an elliptical magnetisedelement of constant thickness that has an alternation of north-southmagnetisation in the directions X and Y.

FIG. 21 shows a narrow rectilinear magnetised element of constantthickness and continuous sinusoidal magnetisation in the direction X anda ferromagnetic part connected to the magnetised element that reducesthe edge effects.

DETAILED DESCRIPTION

FIG. 1 shows a solution of the prior art that makes it possible tomeasure two rotation angles. In this case, the three components of themagnetic field are used to determine the two rotation angles. The magnetused is a cylinder of constant thickness and magnetised only through itsthickness. This very specific configuration is only intended formeasuring two angles and for very small travels since this constantmagnetisation through the thickness is not appropriate for measuring anangle greater than around 30 degrees.

FIGS. 2 a, 2 b, 25 are perspective, front and side views of magnetisedelements (1) and probes (6) used in our embodiments for determining theposition (x,y) of the magnetised element (1) with respect to the probe(6) respectively in a rotation and a translation (FIG. 2 a), twotranslations (FIG. 2 b) and two rotations (FIG. 2 c). Whatever theembodiment of the invention, the probe 6 moves with respect to themagnetised element 1 while remaining in a movement surface and withoutundergoing any rotation about the axis normal to this movement surface.In addition, in the embodiments in FIGS. 2 a, 2 b, 2 c, 3 to 6, 10 to 14and 18 to 21, the distance separating the movement surface of the probefrom the top surface of the magnetised element 1 is constant.

Consequently the movement surface of the probe 6 consists of a portionof a cylinder coaxial with the cylindrical top surface of the magnetisedelement 1 in the embodiments in FIGS. 2 a, 13 and 19, by a flat portionparallel to the flat top surface of the magnetised element 1 in theembodiments in FIGS. 2 b, 3 to 6, 10 to 12, 14, 18 and 20 to 21, and bya portion of a sphere concentric with the spherical top surface of themagnetised element 1 in the embodiment in FIG. 2 c. On the other hand,in the embodiments in FIGS. 15 and 16, in which the probe 6 moves in amovement surface consisting of a plane parallel to a midplane of themagnetised element 1, the distance between the probe 6 and the non-flattop surface of the magnetised element 1 changes, to within a positiveconstant, as a sinusoidal function of the relative positions of theprobe 6 and magnetised element 1 in each of the directions X and Y forthe embodiment in FIG. 15, and in the direction X with the embodiment inFIG. 16. Likewise, in the embodiment in FIG. 17, in which the probemoves in a movement surface consisting of a plane parallel to a fixedplane of the magnetised element 1, the distance between the probe 6 andthe non-flat top surface of the magnetised element 1 changes, to withina positive constant, as a pseudo-sinusoidal function of the relativepositions of the probe 6 and magnetised element 1 in the direction Y.

O is the centre of rotation in the case where a direction is a rotation,O′ is the middle of the external surface of the magnetised element,{right arrow over (O′O)} is zero in the case where the two directionsare translations but O′O=R_(ext) n in the other cases with R_(ext) beingthe external radius of the magnetised element. M is the point where themagnetosensitive elements are grouped together in the probe (6) and A isthe projection of M along the normal vector {right arrow over (n)} onthe external surface of the magnetised element (1). O(ī, j, n) is thereference frame used for defining the position of the various points O′,A and M. In the case of FIGS. 2 a, 2 b and 2 c, the reference frame isrespectively a cylindrical, Cartesian and spherical reference framewhere {right arrow over (n)} is the normal vector at a point on asurface and ī, j the vectors tangential to this surface at this samepoint. The vector {right arrow over (AM)} is therefore colinear with thevector {right arrow over (n)} at A and its norm corresponds to themeasurement air gap z0, which is a constant of the sensor. FIGS. 2 a, 2b and 2 c indicate to us that {right arrow over (OM)}=R_(ext) n+xī+yī+z₀n. The purpose of the present invention is therefore to determine thepair (X,Y) in order thus to determine the position of the magnetisedelement (1) with respect to the magnetosensitive elements (2) and (3) ofthe probe (6) in the two directions oriented by the vectors {right arrowover (i)}, {right arrow over (j)}.

In these FIGS. 2 a, 2 b, 2 c, the dimensions of the magnetised element(1) in relation to the reference frames ī, j, {right arrow over (n)} aredefined for each configuration. For the case in FIG. 2 a, it is aquestion respectively of the rectilinear length, the angular length andthe thickness. For the case in FIG. 2 b, it is a question respectivelyof the length, the width and the thickness. For the case in FIG. 2 c, itis a question respectively of the first angular length, the secondangular length and the thickness.

FIG. 3 shows a plan view of an embodiment where the sensor is composedof a parallelepipedal magnetised element (1) of length Lx and width Ly,and of centre O(0,0,0), and a probe (6) capable of measuring atM(x,y,z0) the three components of the magnetic field (Bx, By, Bz)generated by the magnetised element (1) in order to derive therefrom theposition (x,y) in the directions X and Y of the element (1) with respectto the probe (6). The travel of the magnetised element (1) along X is(2xmax) and along y is (2ymax) with 2xmax and 2ymax substantially equalto respectively Lx and Ly.

FIG. 4 shows the magnetised element (1), the probe (6) and the component(Bx) of the magnetic field at any point M(x,y,z0) and at a givenmeasurement air gap z0, obtained with a magnetisation of the magnetisedelement (1) according to one of the embodiments described by thispresent invention. In this case, the magnetised element (1) generates amagnetic field the component Bx of which varies sinusoidally in its twodirections X and Y so that

${{Bx}\left( {x,y,z_{0}} \right)} = {{Bx}\; {MAX}\; {\cos \left( {\frac{2\pi}{Lx}x} \right)}*{\cos \left( {\frac{\pi}{Ly}*y} \right)}*{\frac{A}{zo}.}}$

FIG. 5 shows, according to the same configuration as the previousfigure, the component (Bz) of the magnetic field at any point (x,y) andwith a measurement air gap z0 and which can be written:

${{Bz}\left( {x,y,z_{0}} \right)} = {{Bz}\; {MAX}\; {\sin \left( {\frac{2\pi}{Lx}x} \right)}*{\cos \left( {\frac{\pi}{Ly}*y} \right)}*{\frac{A}{z\; 0}.}}$

FIG. 6 shows, according to the same configuration as the two previousfigures, the component (Bz) of the magnetic field at any point (x,y) andwith a measurement air gap z0 and which can be written:

${{Bz}\left( {x,y,z_{0}} \right)} = {{Bz}\; {MAX}*\; {\sin \left( {\frac{2\pi}{Ly}*x} \right)}*{\cos \left( {\frac{\pi}{\lambda_{x}}*x} \right)}*{\cos \left( {\frac{\pi}{\lambda_{x}}*y} \right)}*{\frac{A}{z\; 0}.}}$

FIG. 7 shows the change, in the direction X—in mm—of the component By—inGauss—of the magnetic field generated by the magnetised element (1)according to one embodiment of the present invention and with a givenair gap z0, for 8 positions according to different Ys. In this casexmax=10, ymax=4, Bymax=400, phi=0, λ4=20 and λ2=4 and A=z0.

FIG. 8 describes the processing of the field B generated by themagnetised element (1) and measured by the probe (6) which, from atleast two of these magnetosensitive elements (2) and (3) that aresituated at the same point, make it possible to measure the threecomponents of the magnetic field. Once these three components have beenobtained, the processing circuit (5) makes it possible, from algebraiccombinations between the components and calculation of angle andmodulus, to determine the position along X and Y of the magnetisedelement with respect to the probe. The processing circuit (5) can beintegrated in the probe (6) or be done outside via a microcontroller oran ECU.

FIGS. 9 a, 9 b, 9 c show different algorithms for postprocessing of thecomponents Bx, By, Bz in order to determine the position of themagnetised element with respect to the probe (6) along X and Y,according to the type of magnetised element and magnetisation chosen.FIG. 9 a shows how to use the three components of the magnetic field bycalculating A tan (K1Bx/Bz) and A tan (K2By/Bz) in order to determinethe position x and y. FIG. 9 b shows how to use only two components ofthe magnetic field by calculating A tan(K1Bx/Bz) and the modulus(root(Bx̂2+Bẑ2)) in order to determine the position x and y. FIG. 9 showshow to use the three components of the magnetic field by calculating Atan(root((K1Bz)̂2+(K2By)̂2)/Bx) and A tan(root((K1Bz)̂2+(K2Bx) ̂2)/By) inorder to determine the position x and y.

FIG. 10 shows an output signal according to one embodiment of thepresent invention that makes it possible to determine the position alongX independently of the position along Y from the components Bx and Bz ofthe magnetic field as shown in FIGS. 4 and 5 and using the processingdefined in 9 a. The output signal is obtained by calculating thearctangent of (Kx*Bx/Bz), which gives a linear output signal along X andindependent of Y, whatever the measurement air gap z0, which makes itpossible to determine the position of the magnetised element (1) withrespect to the probe (6) in its direction X.

According to the same principle, FIG. 11 shows an output signal thatmakes it possible to determine the position along Y independently of theposition along X. The output signal is obtained by calculating thearctangent of (Ky*By/Bz), which gives a linear output signal along Y andindependent of X, whatever the measurement air gap z0, which makes itpossible to determine the position of the magnetised element (1) withrespect to the probe (2) in its second direction Y.

FIG. 12 shows a rectilinear magnetised element (1) of constant thicknessand with magnetisation, represented by the vector {right arrow over(M)}, the direction of which varies linearly in several directions inplanes defined by combination of the movement directions X and Y andnormal to these directions, that is to say Z. In this figure and all thefollowing figures, a solid arrow in the magnetised element (1)represents a magnetisation direction along the axes or {right arrow over(n)} of the reference frame defined in FIG. 2 b, a dotted circlerepresents an outgoing magnetisation direction and a crossed circlerepresents an incoming magnetisation direction. As can be seen, thefield lines thus defined in the magnetised element (1) are non-colinear,which constitutes one of the basic principles of the said invention andmakes it possible to generate components of the magnetic field such asthose in FIG. 4 or 5 or 6 but with phi=pi/2 and whatever the dimensionsof the magnetised element.

FIG. 13 is a perspective view of a tile magnet (1) of constant thicknessand with magnetisation, represented by the vector {right arrow over(M)}, the direction of which varies linearly in several directions inplanes defined by combination of the movement directions X and Y andnormal to these directions, that is to say Z. As can be seen, the fieldlines thus defined in the magnetised element (1) are non-colinear, whichconstitutes one of the basic principles of the said invention and makesit possible to generate components of the magnetic field such as thosein FIG. 4 or 5 or 6 but with phi=pi/2 and whatever the dimensions of themagnetised element. In this case X is a rotation direction and Y atranslation direction.

FIG. 14 shows an embodiment applied to a rectilinear magnetised element(1) of constant thickness. According to this particular embodiment, themagnetised element (1) has a magnetisation, represented by the vector{right arrow over (M)}, the direction of which varies linearly along thelength of the magnetised element in a plane defined by the movementdirection X and a normal to this direction Z. As can be seen, the fieldlines in the magnetised element are non-colinear, which constitutes oneof the basic principles of the said invention and makes it possible togenerate components of the magnetic field such as those in FIGS. 4, 5and 6 in the case where the width of the magnetised element Ly is small.

FIG. 15 shows a circular magnet (1) of thickness variablequasi-sinusoidally along its radii and magnetised substantially acrossthe thickness (direction z). This embodiment makes it possible, whateverthe dimensions of the magnet, to generate magnetic fields such that:

Bx(x,y,z0)=BxMAX*cos(2pi/λp*x+phi)*cos(2pi/λx*y)*A/z0

By(x,y,z0)=ByMAX*sin(2pi/λp*x+phi)*sin(2pi/λ*y)*A/z0

Bz(x,y,z0)=BzMAX*sin(2pi/λp*x+phi)*cos(2pi/λ*y)*A/z0

where phi=pi/2 and λu=xmax and λe=ymax. Calculation of the arctangent ofKxBx/Bz or KyBy/Bz performed by (5) gives a linear signal and givesinformation on the position of the magnet with respect to the probealong the two axes X and Y.

FIG. 16 shows a magnetised element (1) having a magnetisation thedirection of which is substantially oriented across its thickness butthe thickness of which varies quasi-sinusoidally. According to thisembodiment, if the width Ly of the magnetised element (1) is small, themeasured components of the magnetic field are such that

Bx(x,y,z0)=BxMAX*cos(2pi/λp*x+phi)*cos(2pi/λx*y)*A/z0

By(x,y,z0)=ByMAX*sin(2pi/λp*x+phi)*sin(2pi/λ*y)*A/z0

Bx(x,y,z0)=BzMAX*sin(2pi/λp*x+phi)*cos(2pi/λ*y)*A/z0

where phi=pi/2 and λh=xmax and λe=ymax. Calculation of the arctangent ofKxBx/Bz or KyBy/Bz performed by (5) gives a linear signal and givesinformation on the position of the magnet (1) with respect to the probe(6) along the two axes X and Y.

FIG. 17 shows a magnet (1) the thickness of which varies discontinuouslyalong Y and which has a sinusoidal magnetisation along X. At a large airgap between the magnetised element and probe (6), the components of themagnetic field become continuous again and we can calculate thearctangent of KxBx/Bz and the modulus of (Bx+Bz) in order to derivetherefrom the position of the magnetised element (1) with respect to theprobe (6) in its two directions X and Y.

FIG. 18 is a side and plan view of a magnetised element (1) thethickness of which is constant and has a magnetisation through itsthickness but the amplitude of which is sinusoidal in the direction X.This case is well suited to the use of an anisotropic magnet with regardto the magnetised element (1). Anisotropy across the thickness makes itpossible to have magnets having a higher remnant induction. Given that,in this case, we have no variation in magnetisation in the direction Y,this case functions in the case where the anisotropic magnet is narrow,profiting from the edge effects.

FIG. 19 is a perspective view of a magnetised tile element (1) ofconstant thickness and a diametral magnetisation where the direction Xis a rotation and the direction Y is a translation. This diametralmagnetisation corresponds well to a magnetisation direction that isvariable with respect to the thickness and in this case in the directionX. Given that in this case we have no variation in magnetisation in thedirection Y, this case functions in the case where the magnetisedelement (1) is narrow, acting on the edge effect. It is also possible,for this case, to use a diametrically anisotropic magnet.

FIG. 20 shows a view in section and perspective of an ellipticalmagnetised element (1) of constant thickness that has a magnetisationalong Z and discontinuous with an alternation of North and Southmagnetisation along the axis X and Y. This magnetisation causes acertain distance of the magnetised element (1) from the components Bx,By, Bz of the magnetic field, as described in FIGS. 4, 5 and 6.

FIG. 21 shows an embodiment of the magnetisation applied to arectilinear magnetised element (1) of constant thickness. According tothis particular embodiment, the magnetised element (1) has amagnetisation (represented by the vector {right arrow over (M)}, thedirection of which varies linearly along the length of the magnet in aplane defined by the movement direction X and a normal to this directionZ. In addition to the magnetised element, a ferromagnetic part (7) isadded in order to increase the field generated by the magnetised element(1) and to reduce the edge effects in the direction X.

As will have been understood by a person skilled in the art from areading of the present description, the invention concerns a magneticposition sensor making it possible to determine the bidimensionalposition of a probe 6 able to move with respect to a magnetised element1, including in the case where the movement of the probe has highamplitude in at least the first of the two movement directions. To dothis, the invention can use one or more principles chosen from a set ofthree principles. The first principle, which can be applied to thedetermination of the position of the probe in the first dimension oreach of the two dimensions of the bidirectional movement, consists ofproviding the magnetised element with a magnetisation producing amagnetic field that is at least approximately sinusoidal in,respectively, this first dimension or each of the two dimensions.

The second principle, which can only be applied to the determination ofthe position of the probe in the second dimension of the bidirectionalmovement and only in the case where the amplitude of the movement inthis second dimension is limited, consists of estimating the position ofthe probe in this dimension and using the measurement of anapproximately sinusoidal magnetic field produced by the magnetisedelement by virtue of an edge effect. The third principle, which can beapplied to the determination of the position of the probe in the firstdimension or each of the two dimensions of the bidirectional movement,consists of estimating the position of the probe in this first dimensionor each of them using the measurement of a magnetic field of variableintensity produced by the magnetised element having a constantmagnetisation direction in the first dimension or each of the twodimensions of the bidirectional movement.

This third principle can itself be implemented according to twodifferent modes. The first mode, for example described with reference toFIGS. 15 to 17, consist of giving to the top surface of the magnetisedelement a sinusoidal or pseudo-sinusoidal form along the first dimensionof the movement or each of them, so that the distance between the probe6 and the top surface of the magnetised element 1 varies according tothe position of the probe in respectively the first dimension or each ofthem. The second mode, for example described with reference to FIG. 18,consists of providing the magnetised element with a magnetisation thatvaries in intensity in one of the two dimensions of the movement.

1. A magnetic position sensor in at least two directions comprising: atleast one magnetised element and a probe comprising at least twomagnetosensitive elements located substantially at the same point andeach measuring one of the components of the magnetic field generated bythe magnetised element, the magnetised element being able to moverelative to the magnetosensitive elements, and at least one processingcircuit able to make calculations of angles and moduli from algebraiccombinations of the components of the magnetic field and supplying atleast two independent signals representing the position of the movableelement in respectively each of the two directions; the magnetisationvector of the magnetised element being variable with respect to thevector normal to the surface of the magnetised element disposed oppositethe probe on at least a first one of the dimensions of the magnetisedelement so as to define a unique position of the probe vis-à-vis themagnetised element in the first dimension.
 2. A magnetic position sensoraccording to claim 1, wherein the direction of the magnetisation vectorof the magnetised element is variable in at least one of the dimensionsof the magnetised element.
 3. A magnetic position sensor according toclaim 2, wherein the direction of the magnetisation vector has severalperiods over the travel measured.
 4. A magnetic position sensoraccording to claim 1, wherein one of the dimensions of the magnetisedelement is variable in at least one of the two directions causing avariation in the direction of the normal vector.
 5. A magnetic positionsensor according to claim 4, wherein the dimension varies according to adiscontinuous function.
 6. A magnetic position sensor according to claim4, wherein the dimension of the magnetised element varies substantiallyaccording to a sinusoidal function.
 7. A magnetic position sensoraccording to claim 1, wherein the amplitude of the magnetisation vectorof the magnetised element is variable in at least one of the twodirections.
 8. A magnetic position sensor according to claim 1, whereinthe direction of the magnetisation vector is constant and its amplitudevaries sinusoidally in at least one of the two directions.
 9. A magneticposition sensor according to claim 1, wherein the magnetisation vectorof the magnetised element has at least one alternation in direction inat least one of the two directions.
 10. A magnetic position sensoraccording to claim 1 wherein the signal processing circuit makes atleast two arctangent calculations.
 11. A magnetic position sensoraccording to claim 1, wherein the signal processing circuit makes atleast one arctangent calculation and one modulus calculation.
 12. Amagnetic position sensor according to claim 1 wherein the calculation ofthe position in at least one direction is made by an arctangentcalculation of the ratio of two components of the magnetic field afterhaving applied a correction coefficient between these two components.13. A magnetic position sensor according to claim 1, wherein theprocessing circuit is integrated with the magnetosensitive elements in asingle component.
 14. A magnetic position sensor according to claim 1,wherein the magnetised element includes a permanent magnet and at leastone ferromagnetic part.
 15. A magnetic position sensor according toclaim 1, wherein the components of the magnetic field measured varysubstantially sinusoidally in each of the at least two directions.